Nix dynamic derivations turn build graphs from fixed plans into runtime decisions

A blog post examines how Nix's dynamic derivations feature fundamentally changes the nature of its build graph, shifting Nix from an 'applicative' system—where every build step is known in advance—to a 'monadic' one, where the graph can be constructed as the build itself progresses. The author revisits earlier writing on the topic after noticing renewed interest, including talks at NixCon 2026 and a new tool called cargo-dyndrv.